Float actuated valves are used to control the flow of water into a cell of a battery for replenishing the aqueous electrolyte that is lost during battery charging. Such batteries typically comprise a casing containing a number of individual cells each holding an electrolyte solution in which plates are immersed. Examples of batteries having an aqueous electrolyte include nickel-cadmium batteries or lead-acid type batteries. Oxygen and hydrogen gases are produced during charging as a result of electrolysis of the water. The gases bubble up through the electrolyte, cause splashing of the electrolyte at its free surface within the cells, and accumulate in a gas space above the plates and the electrolyte. The electrolysis causes a loss of water from the electrolyte solution, and as a result, such batteries require periodic replenishment of the lost water.
Float actuated valves are advantageous because they provide a valve that opens and closes automatically in response to the level of electrolyte within a cell. When the electrolyte level is low, the valve opens to allow water to flow into the cell. The valve closes to halt the flow of water once the desired level of electrolyte is reached. This is accomplished by using a float positioned within the cell to open and close the valve. The float is buoyantly supported by the electrolyte and connected to the valve via an actuating mechanism. When the electrolyte level is low, the float moves downwardly away from the valve and its weight applies a force that acts through the actuating mechanism to open the valve. As water flows into the cell through the open valve, the electrolyte level rises and the float is buoyed upwardly and applies an opposite force to the valve through the mechanism which closes the valve once a desired electrolyte level is reached.
One weakness of float actuated valves currently in use lies in the mechanism that links the float to the valve. This mechanism typically has several moving parts and is prone to stick or jam over time because it becomes fouled with a sticky tar-like residue formed by sulfuric acid reacting with mineral oil which leaches out of the polyethylene material forming the walls of each cell. The residue is deposited on the mechanism when the hydrogen and oxygen bubbles burst at the free surface of the electrolyte. The bubbles splash the residue, which floats on the free surface, onto the mechanism. The residue fouls the parts, which are typically close toleranced sliding components, and prevents them from moving freely relatively to one another, eventually preventing all movement of the float and locking the valve in a closed or an open position. Actual field experience in Europe and the U.S. indicates that present float valves tend to fail in less than 18 months in high temperature or heavy duty service.
Another weakness of float valves is their lack of resistance to progressive hydrogen-oxygen explosions traveling between cells. Typically, the cells are connected in series to one another through the conduit that supplies replenishing water. Most of the valve designs currently in use have a water trap in the valve that is intended to prevent a flash path from developing through the conduit between the cells. Unfortunately, the water does not always remain within the trap. It can evaporate, drain out if the battery is tilted or be forced out by gas pressure that develops within each cell during charging.
Yet another problem associated with current float actuated valves is their lack of a flash arrester for hydrogen gas that vents from the cell to the ambient. Such flash arresters would be effective at preventing a hydrogen-oxygen explosion, but are often not used because they tend to restrict gas flow from the cells which causes a back pressure to develop within the cells. The gases that build up in the cells often find an escape path through the water traps and conduit described above that connect the cells for water replenishment, thus, forming a perfect flash path for a progressive hydrogen-oxygen explosion throughout the cells of the battery.
There is clearly a need for an improved float actuated valve that addresses the aforementioned weaknesses of float valves currently in use.